rs6000: Don't use HARD_FRAME_POINTER_REGNUM if it's not live in pro_and_epilogue (PR91518)

This bug is exposed by FRE refactor of r263875.  Comparing the fre
dump file shows no obvious change of the segment fault function proves
it to be a target issue.
frame_pointer_needed is set to true in reload pass setup_can_eliminate,
but regs_ever_live[31] is false, pro_and_epilogue uses it without live
check causing CPU2006 465.tonto segment fault of loading from invalid
addresses due to r31 not saved/restored.  Thus, add HARD_FRAME_POINTER_REGNUM
live check with frame_pointer_needed_indeed when generating pro_and_epilogue
instructions.

gcc/ChangeLog

2020-04-27  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	PR target/91518
	* config/rs6000/rs6000-logue.c (frame_pointer_needed_indeed):
	New variable.
	(rs6000_emit_prologue_components):
	Check with frame_pointer_needed_indeed.
	(rs6000_emit_epilogue_components): Likewise.
	(rs6000_emit_prologue): Likewise.
	(rs6000_emit_epilogue): Set frame_pointer_needed_indeed.

gcc/ChangeLog

+2020-04-27  Xiong Hu Luo  <luoxhu@linux.ibm.com>
+
+	PR target/91518
+	* config/rs6000/rs6000-logue.c (frame_pointer_needed_indeed):
+	New variable.
+	(rs6000_emit_prologue_components):
+	Check with frame_pointer_needed_indeed.
+	(rs6000_emit_epilogue_components): Likewise.
+	(rs6000_emit_prologue): Likewise.
+	(rs6000_emit_epilogue): Set frame_pointer_needed_indeed.
+
 2020-04-25  David Edelsohn  <dje.gcc@gmail.com>
 
 	* config/rs6000/rs6000-logue.c (rs6000_stack_info): Don't push a

gcc/config/rs6000/rs6000-logue.c

@@ -58,6 +58,8 @@ static bool rs6000_save_toc_in_prologue_p (void);
 
 static rs6000_stack_t stack_info;
 
+/* Set if HARD_FRAM_POINTER_REGNUM is really needed.  */
+static bool frame_pointer_needed_indeed = false;
 
 /* Label number of label created for -mrelocatable, to call to so we can
    get the address of the GOT section */
@@ -2735,9 +2737,9 @@ void
 rs6000_emit_prologue_components (sbitmap components)
 {
   rs6000_stack_t *info = rs6000_stack_info ();
-  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed
-			     ? HARD_FRAME_POINTER_REGNUM
-			     : STACK_POINTER_REGNUM);
+  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed_indeed
+				      ? HARD_FRAME_POINTER_REGNUM
+				      : STACK_POINTER_REGNUM);
 
   machine_mode reg_mode = Pmode;
   int reg_size = TARGET_32BIT ? 4 : 8;
@@ -2815,9 +2817,9 @@ void
 rs6000_emit_epilogue_components (sbitmap components)
 {
   rs6000_stack_t *info = rs6000_stack_info ();
-  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed
-			     ? HARD_FRAME_POINTER_REGNUM
-			     : STACK_POINTER_REGNUM);
+  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed_indeed
+				      ? HARD_FRAME_POINTER_REGNUM
+				      : STACK_POINTER_REGNUM);
 
   machine_mode reg_mode = Pmode;
   int reg_size = TARGET_32BIT ? 4 : 8;
@@ -2996,7 +2998,10 @@ rs6000_emit_prologue (void)
                            && (lookup_attribute ("no_split_stack",
                                                  DECL_ATTRIBUTES (cfun->decl))
                                == NULL));
- 
+
+  frame_pointer_needed_indeed
+    = frame_pointer_needed && df_regs_ever_live_p (HARD_FRAME_POINTER_REGNUM);
+
   /* Offset to top of frame for frame_reg and sp respectively.  */
   HOST_WIDE_INT frame_off = 0;
   HOST_WIDE_INT sp_off = 0;
@@ -3658,7 +3663,7 @@ rs6000_emit_prologue (void)
     }
 
   /* Set frame pointer, if needed.  */
-  if (frame_pointer_needed)
+  if (frame_pointer_needed_indeed)
     {
       insn = emit_move_insn (gen_rtx_REG (Pmode, HARD_FRAME_POINTER_REGNUM),
 			     sp_reg_rtx);
@@ -4534,7 +4539,7 @@ rs6000_emit_epilogue (enum epilogue_type epilogue_type)
     }
   /* If we have a frame pointer, we can restore the old stack pointer
      from it.  */
-  else if (frame_pointer_needed)
+  else if (frame_pointer_needed_indeed)
     {
       frame_reg_rtx = sp_reg_rtx;
       if (DEFAULT_ABI == ABI_V4)